Currently, sepsis at different life stages, neonatal, childhood, or in adults, is a leading cause of death globally. Neonatal sepsis, in particular, presents vague signs and symptoms; therefore, current management of neonatal sepsis requires a high index of suspicion, even on the part of highly trained clinicians. For example, one presenting sign may only include an alteration in feeding behavior. Further, the use of antibiotics must be carefully calculated as the inappropriate use of antibiotics leads to the emergence of resistant strains of pathogens.
The sustained increase in antibiotic resistance (ABR) is a major concern worldwide that is affecting patient outcomes causing significant increases in morbidity and mortality. As per the 2015 World Health Organization (WHO) report on current practices in place to address ABR, many governments have initiatives, but there are major discontinuities in action across all 6 WHO regions and many low-income countries do not have a response plan. A recent review has estimated 10 million deaths worldwide and economic loss of around $100 trillion due to drug-resistant infections. The Centers for Disease Control and Prevention (CDC) reports that almost 50% of antibiotics prescribed for people are not required and also not effective. Additionally, the CDC reports that each year in the U.S., at least 2 million people acquire bacterial infections resistant to one or more antibiotics and at least 23,000 people die each year as a result.
Traditional minimum inhibitory concentration (MIC) assays are performed by diffusion or dilution methods. Diffusion method involves a hydrophilic strip or disc infused with antibiotic that is placed in contact with the agar plate surface on which a microbe is cultured. The MIC is estimated based on a visual ‘zone of inhibition’ around the disc or strip. The analyses of results obtained by diffusion method are subjective and variable. In dilution method, a series of culture tubes or agar plates with nutrient media and serial dilution of an antibiotic are used to grow bacteria. The MIC is determined by visual inspection, by identifying the lowest concentration of antibiotics that inhibits bacterial growth. The guidelines for determining MIC by dilution-based methods have been published by the Clinical Laboratory and Standards Institute (CLSI) in the U.S.
The majority of quantitative ABR evaluation is done via automated systems that are not portable and rely on some variant of traditional microdilution testing. Conceptually, in these systems, the bacterial sample is split and exposed to an array of different antibiotics and doses. The plate or card is incubated for a period of time and then read to determine the MIC of each antibiotic that halts cell growth. The specifics of the assay and their read out format vary from manufacturer to manufacturer (see the Vitek II, Brilliance™ ESBL, MicroScan WalkAway, Phoenix, and Sensititre systems), but generally require at least 16 to 24 hours for obtaining final susceptibility results depending on the organism.
Several microfluidic implementations of diffusion/dilution methods have been reported to reduce assay time and rely on applying plugs of fluids, concentration gradient generators, microparticles and dielectrophoresis. However, these approaches require multiple steps, technician training and other external equipment such as syringe pump, which are barriers to translating these devices to clinical applications and point-of-care diagnostics. There is a need for a point-of-care MIC assay technology that does not require external equipment, can be operated without extensive user training, and can measure the MIC of various antibiotics with required specificity/sensitivity in a cost-effective manner.
Technological advancements, especially in the medical field, seldom reach resource-limited populations. For example, current medical diagnostic equipment can be costly, bulky, and require sophisticated training to operate and maintain. Therefore, there is a need in the art for a point-of-care molecular diagnostic device that can identify infectious disease pathogens and antibiotic resistance quickly and with little skill required such to enable health workers around the globe appropriately refer and manage infections and sepsis.
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